Breechblock

This is a real huge construction. It can be opened by upward moving. There is the inscription on the breachblock body: "406 mm. 50 cal. Barrel weight with breech and block - 129200 kg. Barrel weight - 126058 kg. Breach #4. Bolster #4. Liners #2-1.". "50 cal" means that barrel length is 50*406.4=20320 mm.